Palin later accused Biden of raising "the white of flag of surrender" in Iraq over the Democrat policy of withdrawing US forces from the country.

Biden said the Republicans were not offering a plan to end the conflict, triggered by the US-led invasion of Iraq in March 2003, in which tens of thousands of Iraqis and more than 4,000 US troops have been killed.

Marwan Bishara, Al Jazeera's senior political analyst, said that was where the contrast between the two was most clear and that Palin did not define what a US victory would mean.

The debate focused heavily on foreign policy, considered by many analysts to be a weak point for Palin.

Both candidates discussed Afghanistan, Pakistan and Iran as well as pledging their support for Israel.

Robert Fisk, the author and Middle East correspondent of the UK's Independent newspaper, said the debate showed how both campaigns ignored the plight of the Palestinians.

"The Palestinians were deleted from the narrative. There was no reference to Jewish settlements, built illegally on Arab land. There was not the slightest reference to the Israeli occupation on the West Bank."

Biden later also lashed out at Dick Cheney, the current vice-president, calling him "the most dangerous vice-president in American history".

Republicans falter

Thursday's debate came after a poll found that most US voters have huge doubts about Palin's experience and her ability to lead.

Millions of Americans watched the debateon television [AFP]

"Six in 10 voters see her as lacking the experience to be an effective president, and a third are now less likely to vote for McCain because of her," the Washington Post said of its joint poll with ABC News.

And McCain's campaign, which has stalled in the wake of the global financial crisis, said on Thursday that he had conceded the battleground state of Michigan in order to focus on states where he has a better chance of beating Barack Obama, the Democratic presidential candidate.

"It's been the worst state of all the states that are in play and it's an obvious one from my perspective to come off the list," said Greg Strimple, a senior McCain adviser.

Concerns over Palin's experience have increased since she gave a series of interviews on foreign policy, the economy and the US supreme court.

She has faced ridicule for some of her answers, including citing Alaska's proximity to Canada and Russia as valid foreign policy experience.